Sudden death syndrome (SDS) is being reported from several areas of the state. In Putnam County, Charlie Frank of G & J Fertilizer reports several SDS fields; and Mike Roegge, Extension educator from Adams/Brown, reports SDS on the increase as well.|
Weather conditions were favorable for SDS infection this spring in many areas of the state. Infection by the Fusarium fungus that causes this disease occurs about 30 days after planting. Although generally we had a fairly dry spring for planting, we did have some timely moisture around SDS infection time. We have had record levels of SDS in Illinois in the past several years, so watch for this disease in the next several weeks. The good news from an impact perspective is that the later in the season the aboveground symptoms appear, the less yield loss you can expect. When aboveground symptoms are evident, the seed will not mature any further.
Although SDS is actually a root disease, it's the very dramatic foliar symptoms that generate attention first. Foliar symptoms begin as yellow interveinal flecks.
Early foliar symptoms of SDS. (Photo courtesy of Loretta Ortiz-Ribbing.)
The flecks expand and begin to coalesce, and the tissue begins to die. However, the veins remain green. The roots will be rotted, appearing reddish brown with little or no secondary roots remaining. Expect premature defoliation, usually from the top down; and although it isn't diagnostic, the petioles usually remain attached to the stem.
To diagnose SDS, you must split open the stem. Look for grayish-brown streaking of the vascular tissue external to the pith. This is most evident close to the soil line. SDS alone will not discolor the pith tissue. The foliar symptoms of SDS seen in the field are similar to those of brown stem rot, but SDS internal stem symptoms differ, in that there is not the characteristic chocolate-brown discoloration seen in brown stem rot.
Expect SDS to show up first in low spots where other root rots may have been a problem earlier in the season, or in areas of the field where soybean cyst nematode (SCN) has been a problem. Although neither SCN nor other root infections are necessary for SDS infection, they all share similar environmental factors for disease development; so you will mostly likely find them in similar locations. Remember, you must split open the stem to get a definitive diagnosis.--Suzanne Bissonnette